Whether surfing the web, playing video games or watching TV, children's after-school eating habits in front of screens have concerned researchers.

In a New Zealand study, researchers simulated an after-school environment for 20 young boys, providing them with a mixture of high- and low-energy snack foods as they sat down for some screen-time.

The children ate a worrying amount of high-energy food while playing video games or sitting in front of television or computer screens, but it was television watching results which caused most concern.

The study, led by University of Auckland PhD student Samantha Marsh, is thought to be the world's first lab-based trial to compare the energy intakes of boys while in front of each of the three screens.

Afterwards, each reported what they ate and researchers calculated their energy intake while sitting in front of each screen. While viewing TV, where they watched either Man v Wild or MythBusters, the average intake totalled 821 kilocalories - or about half the recommended daily intake.

Importantly, the experiment deliberately excluded food advertisements on TV, proving that children could still eat unhealthily in the absence of marketing. When playing Xbox 360 games or going online, the children's intake was less, but still unhealthy, equating to an average 696 and 685 kilocalories respectively.

"We've shown that kids can still eat a lot while playing video games, even though a lot of parents thought they wouldn't, perhaps because they are constantly using their hands."

In just six years, the obesity rate among children aged between 5-11 has jumped from 8 to 11 per cent.

The research, published in the journal Appetite, will eventually be followed by more work looking at how children eat when using more than one screen at once.